This manual aims at improving the capacity of policy analysts to understand the problems related to food security, and in particular the concept of food security defined as availability, stability and access to food by each human being. The food system, with its mechanism governing the production and transformation of food, is studied with a view to understand the causes of food insecurity. Then, the manual shows how international, macro, and agricultural sector policies affect the food system, and how national and international policies, which could improve food security, can be identified.